An organic light emitting diode (OLED) display is a self-luminous display device that is provided with organic light emitting diodes that emit light to display an image. Unlike a liquid crystal display, the organic light emitting diode display does not require a separate light source, and thus the thickness and weight thereof can be relatively reduced. Moreover, the organic light emitting diode display exhibits high quality characteristics such as low power consumption, high luminance, a high response speed, and the like, and thus is in the spotlight as a next generation display device of a portable electronic apparatus.
FIG. 1 schematically illustrates a general structure of an OLED/pixel unit of an organic light emitting diode display.
Referring to FIG. 1, a positive electrode 20 as a first electrode is formed on a substrate 10 for the organic light emitting diode display, and the positive electrode 20 is divided into pixel units using pixel defining layers (PDLs) 30. A light emitting layer 50 is formed on the positive electrode 20 and a portion of the pixel defining layers 30. A negative electrode 70 is formed as a common electrode on the light emitting layer 50 and the pixel defining layers 30.
Before forming the light emitting layer 50, at least one of a hole injection layer and a hole transporting layer may be additionally formed, and at least one of an electron transporting layer and an electron injection layer may be formed between the light emitting layer 50 and the negative electrode 70. Multiple light emitting layers 50 may be separated into a red light emitting layer, a green light emitting layer, and a blue light emitting layer.
Currently, light extraction efficiency of the light emitting diode display is approximately 20%, which is not satisfactory. In other words, only about 20% of light generated from the light emitting layer of the light emitting diode display is emitted outside through a light emitting surface, and about 80% of light generated from the light emitting layer is confined and extinguished in, or absorbed by, the structure of the organic light emitting diode display.
The extinguished light partially leaks out to the side of the light emitting layer of the organic light emitting diode display. That is, an arrow in FIG. 1 denotes that a part of light generated from the light emitting layer of the organic light emitting diode display is emitted to the side to be incident on the pixel defining layer. As shown in FIG. 1, a part of the light generated from the light emitting layer of the organic light emitting diode display is emitted to the side and is incident on the pixel defining layer, and thereafter is extinguished, whereby a part of the light cannot contribute to light emission of the organic light emitting diode display and leaks out.
If the light leaking to the side is allowed to contribute to the light emission, it is possible to enhance light extraction efficiency of the organic light emitting diode display.